Foetal monitor



NOV 5, 1968 M. sETTLr-:R ETAL 3,409,737

FOETAL MONITOR Filed June 24, 1965 zoK 2 1? 2 2 44 MONITOR 23 45 L2oj lL2o lzo I 47 F 1S. 6 FIS. 5 /nf/xwfulr.'

10M-r .Cfmfz www United States Patent 3,409,737 FOETAL MONITOR MorrisSettler, 590 vNiagara St., and Bert Settler, 723 Queenston St., both ofWinnipeg 9, Manitoba, Canada Filed .lune 24, 1965, Ser. No. 466,634 1Claim. (C l. 179-1) ABSTRACT OF THE DISCLOSURE Foetal heartbeat ismonitored by a plurality of transducers mounted on an elastic belt. Aswitch selects which transducer is fed to the amplifier which has afilter for discriminating between the foetal heartbeat and the mothersheartbeat.

This invention relates to new and useful improvements in foetalmonitors. Y

Occasionally a foetus dies in the womb during labor without sufficientwarning. This may occur in an otherwise normal labor but is more likelyto occur in more specific obstetrical situations.

The alteration of the normal foetal heart rate is an important sign inthe diagnosis of intrauterine foetal distress.

The object of the present invention is to enable the detection of veryweak foetaly sounds against the background of the maternal sounds andmaternal muscular movement during labor.

A further problem of detecting foetal heart sound is the constant changeof position of the foetus in the womb.v

By providing a plurality of transducers, independently connectable tothe amplier, the attendant is provided with a continuous audible orvisible monitoring of the foetal heartbeat during labor.

Our invention also includes a novel belt to hold the transducers inconstant contact with the patient and a resilient link is provided toaccommodate the expansion and contraction of the abdomen during labor.

This is important inasmuch as it is essential to maintain the continuityof the foetal heart sound during a contraction and it also prevents theearly or premature col-l lapsing of the microphones or transducers ifexcessive pressure is encountered. i

Also provided in the amplifier is an output jack to record the foetalheart sounds graphically. It is therefore possible-to providephonocardiography of the foetal heart sounds. A tape recording may bemade of the sounds from the output jack and a pen lrecording may also bemade at the same time which will permit the operator to study visuallywhat has been heard aurally and to analyze more intensively and ingreater depth, the significance of these foetal heart sounds.

The device uses rechargeable batteries and desirably 3,409,737 PatentedNov. l5, 1968 ice foetal heartbeat contrasted to the relativelydslowrise and decay and relatively wide width of the maternal heartbeat.

I The device is useful in diagnosing anticipated caesarian delivery, toobserve the effects of drugs administered to the mother, `on the foetus,to determine the effects of the birth process on the linfant and tomonitor the heartbeat contains two separate batteries. One is requiredto energize the two coupled amplifiers and the other is used to energizethe output stage.

Because of the high gain required, separate power sources are desirableto overcome feed back and interference between the two components.

Another feature of the present device is that it is completelytransistorized and is therefore light, portable and relativelyinexpensive, safe and free from any electric or explosive hazards andsimple and easy to use.

A significant feature of the present invention is the detection andamplifying of the foetal heart sounds to the total exclusion of maternalheart sounds, a fault prevalent in all other foetal heart monitors atpresent in use.

We obtain this result by the selection of a capacitor coupling the twoamplifiers together which is only triggered by the relatively sharp riseand narrow width of a of a foetus being transfused by intrauterine,intraabdominal method.

` In this particular type of operation, due to continuous monitoring, itis possible to monitor the condition of the foetus during the insertionof the needle, plastic tube, and eventually the transfusion of theblood.

A graphic recording of the heart sounds can also be obtained during anoperation of this type which permits subsequent analysis to be made.

With the foregoing in view, and all those objects, purposes oradvantages which may become apparent from consideration of thisdisclosure and specification, the present invention consists essentiallyof the inventive concept embodied in the method, process, construction,arrangement of parts, or new use of the same, as herein particularlyexemplified, in one or more specific embodiments of such concept,reference being had to the accompanying figures in which:

FIGURE 1 is a schematic wiring diagram of the electronic portion of thedevice.

FIGURE 2 is a front elevation of the belt carrying the transducers.

FIGURE 3 is a schematic view of' the belt showing the three positionswitch and the connections to the electronic portion.

FIGURE 4 is a schematic representation of a graphical recording of afoetal heartbeat.

FIGURE 5 is a view similar to FIGURE 4 but showing a maternalheartbeat.

FIGURE 6 is an enlarged longitudinal cross sectional view showing themounting of the transducers within the belt.

In the drawings like characters of reference indicate correspondingparts in the different figures.

Proceeding therefore to describe the invention in detail referenceshould first be made to FIGURE 2 which shows the belt collectivelydesignated 10,

This consists of an elongated length of flexible, nonextensible surgicalbelting or the like 11, having a plurality of eyelets 12' secured to oneend 13 thereof. 1

-A flexible rubber link 14 is secured to the other end lan an eye hook15 is secured to the end 16 of this rubber This hook is adapted to beengaged in any one of the eyelets 12 depending upon the girth of thepatient so that the belt may be snugged secured around the patientsabdomen and yet can extend and contract therewith.

Intermediate the ends of the belt 11 is secured a further length ofbelting 17 by stitching 18, forming a rein,- forcement and havingeyelets 19 formed therethrough to hold the transducers or microphones 20in spaced apart relationship as clearly seen. 1'

In this connection, studs 20' are connected to the rear of thetransducers and engage through the eyelets 19. Electrical conduits 21extend Ifrom these microphones to a common cable 22 and thence to amultiposition switch 23 which is adapted to select and connect any oneof the electrical conduits 21 to the input 24 of the amplifier section.

The switch is shown schematically in FIGURE l and as this switching isconventional, it is not believed necessary to describe same further.

FIGURE 1 shows the electronic circuit relative to the amplifier andincludes two rechargeable batteries 25 and 26.

l 3 The charger input 28, or, alternatively, to power the amplifiers,the positive of the battery 25 being connected to the Bplus-29-andthenegative .of the batteryto the negaive side 30. A o

The battery 26 is specifically for powering the output amplifiercollectively designated 31 which inturn is connected toa speaker 32, thevolume of which maybe adjusted by means of variable resistor 33.l

The amplifier comprises two multistage amplifiers, co1- lectivelydesignated 34 and 35, coupled together by means of a capacitor 36. Theinput 24 is connected to the transistor 37 of the first amplifier 34 andthe signal is then fed to .the second stage transistor 38 and thence tothe third stagetransistor 39.

.ln this connection We use an NPN transistor at stage 37 and connecttheinput to the emitter of this transistor. By ensuring that the polarityatthe input signal is positive, we have found that the sensitivity ofthe device is increased approximately threefold, compared to thesensitivityif the polarity is negative. l

. The output from transistor 39 is then passed through variable resistor40 to one side of the capacitor 36 and thence to the input of the firsttransistor 37 of the second amplifier 35. y

The signal then passes to the second stage transistor 38 of amplifier 35and then to transistor 39 of this amplifier.

From'there the signal passes through transformer 41 to the outputamplifier 31 which is conventional in construction. l -It is sometimesdesirable that the signal be visual rather than aural in order that thefoetal heartbeat is not heard by the expectant mother. This visualrecording enables the operator to count visually by the swing ofmilliammeter 41 in circuit between the primary side of transformer 41and the B plus voltage.

A recording output 42 also extends from the outputof the transistorr39'through smoothing condenser 43 and this recording output may beconnected either, to a pen recorder (not illustrated) or a tape recorder(also not illustrated).

Also provided is an additional speaker outputjack 32 which can beconnected to a remote speaker or station or multiple of speakers orstations which relieves the nurse of the necessity of remaining at thepatients bed- ,side inasmuch as one nursel can monitor a plurality ofpatients at one location.

` The first amplifier 34 triggers the second amplifier 35 through thecoupling capacitor 36 and the value of this coupling capacitor is .suchthat the maternal heartbeat pulses have no effect n the triggeringaction.

FIGURES 4 and 5 show schematically the difference between a'foetalheartbeat pulse and a maternal heartbeat pulse.

The foetal heartbeat pulse is characterized by a relatively steep rise44 and a relatively narrow width 45 whereas the maternal heartbeat ischaracterized by a relatively slow rise 46 and a relatively wide width47.

Y, Thesecharacteristics decide value of the capacitor 36 so that onlythe steep, sharprise of the foetal impulse will trigger the secondamplifier 3S.v

eliminated entirely from thewdevice so that only the foetal heartbeatsare monitored.

The adjustable resistor 40 between the first amplifier 34 and thecapacitor 36 also assists in the selection of the signal strength atthis .point-in order to eliminate the undesirable maternal heartbeatimpulse from the yinstru'- ment. v

In operation, the `belt'is secured around the abdomen of the mother andthe switch 23 is utilized to locate the position of the foetus, bydetecting the point of maximal signal.

Since various modifications can be made tov=the invention hereindescribed within .the scope of the inventive concept disclosed, it isnot intended that protection of the said invention should be interpretedas restrictedv to the modification or modifications or known parts ofsuch concept as have been particularly described, defined, orexemplified, since this disclosure is intended to explain theconstruction and operation of 'such concept, and not for the purpose oflimiting protection to any specific embodiment or details thereof.

Whatwe claim as our invention is:

1. Means for detecting foetal heartbeat comprising in combination anelongated belt, a plurality of transducers mounted upon -said belt inspaced apart relationship, a resilient link secured to one end ofl saidbelt, fastening means on yboth ends of said belt cooperating together tosecure said belt around the abdomen of the patient, said resilient linkpermitting expansion andcontraction of the belt within limits responsiveto expansion and contraction of the abdomen thereby maintaining saidbelt at a relatively constant tension, electrical conduit extending fromeach of said transducers, a multistage switch connected to saidconduits, a further electrical conduit extending from said switch, saidswitch connecting any one of said first mentioned conduits to said lastmentioned conduit, a pair of multistage amplifiers coupled together bymeans of a resistance-capacitance filter, said single electrical conduitfrom said switch being connected to the input of one of saidampliers, anoutput amplifier connected to the output :of the other of saidamplifiers, and speaker means connected to said output amplifier, saidresistance-capacitance coupling ybetween said amplifiers having valueswhereby said second amplifier responds only to pulses having'a steepattack characteristic and a narrow pulse width as characterized by theheartbeat of the foetus.

References Cited UNITED STATES PATENTS OTHER REFERENCES IBM Tech.Disclosure, Respiration Transducer, G.. R. Willis, Novemberl963.. v

KATHLEEN H. CLAFFY, Primary Examiner. R.v P. TAYLOR, Assistant Examiner.

